1. Field of the Invention
The present invention relates to a sensor device, whose output voltage is corrected through digital arithmetic processing, and, in particular, relates to a sensor device which, when the sensor device fails, informs the host system of the failure.
2. Conventional Art
As a conventional sensor device whose output voltage is corrected through a digital arithmetic processing, JP-A-10-281912 (1998) discloses such a pressure sensor device.
The above conventional art does not take into account a failure of a digital arithmetic processor therein.
Prior to the above conventional device, in a sensor device constituted only by analogue circuits, it was rare for the output voltage of the sensor device to stay at an intermediate voltage due to a failure of the sensor device, but rather the output voltage thereof stays at the respective power source voltage. For this reason, when the output voltage of the sensor stays at the power source voltage or the ground voltage, a host system can judge whether the sensor device has failed. Therefore, when such sensor device has failed, the host system can effect a countermeasure toward a fail safe operation.
Even in the sensor device using the digital arithmetic processing as referred to in the above conventional art, output signals in the form of analogue voltage are frequently used in view of compatibility with analogue type sensor devices. Therefore, through arrangement of a D/A converter at an output-circuit, output signals effected by digital arithmetic processing are outputted after being converted into analogue voltage. However, when the digital arithmetic processing unit has failed, the output signals of the digital arithmetic processing unit stay at an intermediate value, accordingly, the output of the D/A converter which is operated by the output signals of the digital arithmetic processing unit is also caused to stay at an intermediate voltage. When the output signals of the sensor device stay at an intermediate voltage, it is quite difficult to judge whether the sensor device is operating normally or is failing by means of only the output signals of the sensor device. Accordingly, it is difficult to judge whether the concerned sensor device is operating normally or failing by means of the host system, which simply monitors the output signals of the sensor device. Therefore, when the sensor device has failed, the conventional host system could not effect a countermeasure toward a fail safe operation. Namely, with regard to such a problem, the conventional art lacks a proper countermeasure.
An object of the present invention is to solve the conventional problem referred to above, and, more specifically, to provide a sensor device using a digital arithmetic processing and outputting analogue voltages, which permits a host system to judge easily whether the sensor device is operating normally or failing.
The above object can be achieved by a sensor device according to the present invention, which comprises a digital arithmetic processing means which performs an arithmetic processing through a program stored in advance therein, means for generating pulses through the program, and means for causing the output voltage of the sensor device to stay at either a power source voltage or the ground voltage when the pulses from the pulse generating means are interrupted.